Process and apparatus for cracking oils



July 2, ,1935. J. s. GALLAGHER PROCESS AND APPARATUS FOR CRACKING OILS Filed April 18, 1928 @nov/mbox f v5 as gasoline.

Patented y July 2, 1.935

John S. Gallagher, Tulsa, Okla., assignorto The Texas Company, New York, N. Y., acorporation of Delaware y Application April 1s, 192s, serial No. 270,820

` Y12 claims. (ci. 19e-6s) This invention relates to an improved process and apparatus for the conversion of heavier oils, having a relatively high boiling point, into lower boiling oils, such as the type commercially known Primarily, the invention has to do with lthe construction and vmode of operation of theiapparatus employed for the heating of the oil and maintaining it under the appropriate conditions to effect the desired conversion. It is a particular object of the invention toprovide for a more even distribution of heat in the conversion zone, and a more efiicient heat transmlssionconl dition in this zone, and also to prevent, to a large degree, the deposition ofl carbon' which usually takest place in such Zone and which is extremely detrimental. i While the invention is applicable yto stills or conversion Zones of practically every type, .itis particularly applicable to a system commonly known as the coil and. drum, in which the oilis first heated 'in' its .passage through a long, continuous coil in la furnace and is theny introduced t into one or more ofv a series'of drumswhere the tra4 main process of conversion takes place. In systems ofthis character the oil is usually raised to :a temperature somewhat above the initial crackr ing point or, say, betweenfll"` and 850 F. in the coil and is maintained at this or only a slightly reduced temperature' in the drum or series of stills.. For this purpose the stills may either be heat-insulated or may receive heat from an external source. The amount of heat applied externally to the stills is necessarily small, or at least, the introduction of heat must be brought about gradually, Without the use of excessive i temperatures, in View of the great danger which.

always accompanies the application of intense heat to a large body of oil under pressure. .Deposition of carbon is bound to take place under k,operatingconditions in common practice and due to its poor heat transmission qualities, hot spots, `Vwhich tend to greatly weaken' the shell of a still,

. are sure to developwherever intense heat'is applied. For this reason'the temperature of the large body of oil in the drum, or seriesrof stills, must be largely maintainedtby the heat' of the incoming charge from the coil and the mild application'of external heat.

videdv to assist in the transmission, Ythroughthe body of oil, of vheatcoming from these sources, it would be extremely difficult to maintain uniforml conditions in the stills, 'and particularly to maintain the desired temperaturek on the oil at the centers of the large bulks contained` in the stills. Furthermore, Yit is now recognized that If no means were pro- Where an effort is made to heat a large'body of Vliquid in a vessel such as a still'by means of heated gases on the outside, there is-a'r tendency to form-a lm of gases on one side of the shell of the vessel and a lm of liquid on the inside and these films offer an excessively high resistance to the transmission of heat. Y

It is toward overcoming these diiiicultieswhich present invention is directed. To this end it is contemplated maintaining the oilA within the which would result in the objectionable separation of the heavier from the lighter constituents,

i but it is preferably of such velocity as to produce turbulence oi the particles of oil in their circulation. The vigorous and rapid circulation of the oil, which is contemplated by the present invention, will not only serve to provide the desired even distribution of heat throughout the entire body ofl oil in the conversion Zone, but will also prevent'to a large degree the deposition of carbon, and will tend to breakup or reduce the thickness of the liquid film on the inside Wall of vthe still. From the standpoint of greater heat transmission eiiiciencyand better distribution, it becomes possible to maintain slightly lower temperatures in the hotter portions" of the heating coil, which in the past have always been a source of trouble.

It is well known that in a coil'type of heater the tubes which go tol make up thelower section of the coil are burned out more frequently than the upper tubes due to the excessiver heat in the lower portion of the furnace and due to the tendency to i` 'heat in the4 drums or stills. Incidentally, they meanstwhichthe present invention contemplates for the production of the rapidi circulation of the oil within the drums is such as to apply additional heat to the oil inthe stills by the conversion of thei mechanical energyiinto heat and this action further yenables the employmentof more moderate temperatures for external application of heatto the stills'.

Obviously, if desired, the usual temperaturey lconditions inthe y vbrought about in these. tendency to accumulate more or less of a stagnant r3 0 to fthe last. `dues may in this Way be forced into the last drum coil and in the still furnace could be maintained and the greater efiiciency in thetransmission and distribution of the heat could be utilized to produce a higher temperature of the oil in the stills with a consequent higher rate Vof conversion. It has been determined by experimentation that the rate of conversion under temperatures inA the neighborhood of 800 F. is doubled for each increase of 22 in the temperature of the oil so that material benefit is derived from the improved heating conditions.V Y

Now, as already suggested, the rapid circulation of the oil has the further advantage ofv tending to keep in suspension the tarry residues or particles of carbon which would otherwise tend to settle out at the bottoms of the stills, or toV deposit on the walls of the stills, and thus cake up and prevent proper heat transmission. This feature is particularly advantageous where a series of interconnected drums are employed. In` isystems vof ythis character it is commonly the .practice to provide for thepassage of the oil from one still into theV next by means of a line just below the liquid level ofy the oil in the stills.

Fresh oil from the-coil is introduced continuously into the bottom of the rst still, or perhaps of the first two. stills, so that a slight circulation is pool of oil in the remaining drums of the series.

Y'This then leads to a condition of over-cracking ofthoseportions of the oil which remain in vthe stills for an undue length of time with the result that an excessive amount of carbon is formed. While the occasional withdrawal 'of the bottoms `orftarry residues lfrom all of the stills will tend -to `alleviate this condition, it is by no means as satisfactory as the provision of positive means for circulating the 'oil within each still. When such :means are employed, the oil which passes from one still Vinto the next, through the liquid levelling lines toward the tops of the stills, will be representative of theentire bodyof oil in the still from which itflows.

This will naturally tend to effec- .tively bring about the maintenance of successively heavier mixtures of oil in the. drums 'from the vfirst Most of the objectionable tarryresifof the series and it will be possible to provide for the continuous withdrawal of these residues from this still. There will be no tendency to clog up the-passageway by means of the. coky and tarry deposits, since these constituents will be lheld in Vsuspension in the somewhat lighter residual oil up tothe time of withdrawal from the still. While `this may lead to the removal kof some of the lighter oil which could possibly be retained for 'further cracking, the advantage derived from the 'uniformity of operation clearly over-balances this objection.

vUnder the practice now commonly followed, this uniformity of operation is not possible since residues must, as a rule, be drawn off occasionally .from all ofthe stills and for this reason, as well ias fto preventthe clogging Vof the tar-drawing 4lines by virtue of the heavy tars which ordinarily collect in the bottomsof the stills,V the drawing:v lof tarcan usually only be brought aboutat interfractions which may be recycled into the system,A the load on the tar stripper is continually uctu- However, there is a drum Ato the other.

ating and it is impossible to maintain any uniformity in the output of the latter. However, Whereit is possible to continually Withdraw a stream of residue from a single one of the battery of stills, as in accordance with the present invention, it is a simple matter to maintain uniform operating conditions on the tarrstripping unit. This results inthe production of a recycle stock which is of uniform consistency and which may be more readily' handled directly in the same `cracking operation. At the samey time the elimination of the shock on the main stills, which normally occurs at tar drawing periods, serves to improve the operation of the entire system.

-It will -be apparent from the foregoing that through vthe application of the present invention, a more constant product will result and the length of continuous runs between periods of shut-down will be greatly increased.

With these and other incidental objects and advantages LVin view, one suitable form of the invention will now be described in detail, `.with reference to the accompanying drawing -which forms a part hereof.

vThe' single -figure of the drawing illustrates.

diagrammatically an illustrative form of apparatus which maybe employed for the conduct of thernovel process. 1 l

Referring to the drawing, a ,pump YIll is provided for the purpose of drawing voil from any suitable source, and of any suitable character `for This-coil is located Vin a furnace I2 which maybe heated by any suitable means, such as an oil or gas lburner I3.

After the oil has been heated under pressure to a point slightly above a cracking temperature, it maybe passed by the transfer line I4 into one or more of a series of drums or stills Il.l If desired, only a single drum need be employed, although itis regarded as preferable to employ a plurality of, say, three or four. Suitable vapor lines 'I6 and liquid lines llserve to connect the drums in series'so that the generated Ivapors andthe rliquid body of oil maybe passed successively from one If desired, the stills may merely be heat-insulated, although it is regarded as preferable to mountV them in a suitable furnace i8, lwhich is adapted to apply heat externally to the mid-portions of the stills. Vapors of lower Iboiling-oils, which aregenerated inthe several stills, may be conducted by a vapor `line I9 to a dephlegmator or fractionating tower 20, which may be of any `suitable construction and may, for example, be a -bubble tower. A portion offthe vapors will beacondensedinthis tower but Vthose which persist in vaporform will pass out atthe top into a refluxing condenserZl and some ywill continue to the final condenser 22 and the vstorage receptacle :23.

heat exchanger forfthe `purpose of raising the temperature of the fresh charge before the latter is `introduced-'into the coil H.

From` the 'base of the yfractionating tower, va line 24 willserve to conduct :those :portions of the --original vapors .which have rbeen condensed thereinY toga pump 25, which. is connected `by a line 126 to thecoil I I. The `condensate which is -recycledin this `way mayeither `be introduced into the upper end Yof the coil il, together `with :theifresh charge, ormay be Iintroduced at alower point where its :temperature corresponds kmore nearly v'to ythat of .the charge. 'Suitable valves i 21 may be provided foi-"controlling A'Tar draw-off lines jbaseportions of each ofl the stills l tofpermit "f2','006,'42i9 v Ybut the use of individual motors is deemed prefthe lintroduction of this condensate.'V

' v28 are provided'fromthe the4 withdrawal, from time-to time, of the heavy residual oil whichV may tend to collect at'the base or auxiliary still 25 whereinthe' pressure will b e materially reduced and a large portion of the residues will be vaporized under the lower pressure. Vapois so generated may be led through a line 3|] toa dephlegmator or fractionating column 3l which may be provided at the' top with a vsuitablerefluxing condenser 32', from whichA the Vvapors may be passed to a i'lnal condenser 33 and collection receptacle 34. The heavier portions of the vapors generated in thestill 29 will -be `condensed inl the dephlegmator 3l and may be passed by a line'35, pump 35 and line 3l to some suitable point in the main cracking system; lor

.prevent deposition of carbon or tarry matter, par- :ticularly on'these walls. The heavy tars example, the line 3l may join the line 2,6 so that -v-condensates from the two dephlegmators 25- and -3|- may be handled together. s v which collect inthe base of the chamber 29,and

v are not volatilized under the reduced pressure,

may be withdrawn through a line 38 and sentyto suitable storage, or,l ify desired, may be further treated by a process o1 steam distillation or Vthe like. v v

I: -All of the features which havebeen describe r`in detail in the foregoing sections are matters of more or less' known practice, and they are setV forth'here merely for the purpose of better indicating the'nature and utility of the novel features whichrare contemplated bythe Vpresent invention i and which will now be described. It will beunderstood that the features to be described serve to improve the operationv of the foregoing system L and make it more practicable to operate in the 'manner indicated. Y

within each of the stills :s there is provided a long, tubular shell 39 rwhich serves to divideeach stillA into an inner and outer channel. These j'shells may be of any suitable dimension, `but preferably will have a diameter of substantially more than half ofi the inside Adiameter of the stills.

tion in the passageway, as indicated at 39m.` AThey "will be suitably supported by angle members, or

. ing motors 42.

gether with suitable gearing and otherfconnectionsmight be provided Itodrive all of the'shafts the like, within the stills lso as to` have their upper-ends slightly below the liquid levelv and their totipwhich is slightly less than the inside difameters of the shells. It will be understood that l the shaftslll Aare passed through suitable stuillng boxes in the upper ends of the stills toprevent leakage of the vapors and at their upper ends theyareconnected'in any suitable way to driv- If desired, asingle motor; to-

erable. Y

In the operation oi the system, the body of oil `maintained in. eachv of the stills willibe kept in constant circulation` by means of the propellersi ll. `The action'of theVA latter is to suck in the upperportions ofthe oil through the upper ared ends of the shells 39 and to force the oil downwardlythroug'h-the shells and out at the bottoms of the latter. This oil will then necessarily b-e forced upwardly through the passageway between theshells and the inner walls ofthe stills and will be returnedfor circulation in the same way.V By providingl shells ofthe appropriate diameter, the speed of the oil in passing through the channels between thekshells and the inner `walls of the stills may be raised to any extent desired. It'w'ill be clear, therefore', that bythe Ause of this system `there rwill be brought about a very rapid circulation of the oil toy distribute the heat of the incom- .ingv charge, as well as thatfexte'rn'ally applied throughthe walls of lthe stillsto all portionslof theioil, and, furthermore, the rapid movement of the 'oil will not only bring about more efficient heat transmission, due to partly breaking upr the liquid filmv on the inside of thestill walls, but will As a further aid to the transmission of heat from the gases on the outside of the stills to the liquid within, the protective orM heat insulating lm of gases which forms on thefouter surfaces oi' the stills may be brokenl up in any suitableway by the provision of mechanical agitating devices l or means*fordirectingthe gases in sucha manner'asfto effect the desired result.

`Without intending to restrict the scope of the inventioniin any way, some suitable figures concerning theY construction and method oi operation of the system may here be suggested as illustrative. The stills I5 may have a diameter oi, say, 5 feet'and be provided with shellsA 39 having a diameter of 4 feet, thus leaving an annular spaceof, say, 6 inches 1in width. The propellers 40 may have'san overall dimension of, say, 40 inches and may be driven at a speed between 300 and 1200 R. P. M., although speeds'outside rof this VrangeV maybe permissible. It is contemplated that the displacement of the oil will be such as to l provide a velocity of from' l0 to 15 feet Aper second through the annular passageway between the shell 39'sand the wall of the still. YThis velocity should be sucient through the relatively narrow channel to produce a state of turbulence of s the oilY sothat it will become completely intermixed andwill no longer flow inregular', Well del v ned layers orstreams. LIn this way the breaking up of the lm of oil adjacent the'wall' ofthe still will be quite effectively brought about. Preferably the main conversion units will be operated under pressures of between 100 "and500 pounds,

` while the tar strippingunit may be operated at a pressure onlyslightly above atmospheric. Upon leaving thecoil Il, the oil may have a temperature of between '750 and i575" F., preferably 825 F., and in the stills I5 this temperature should be substantially maintained, although a drop of, say, 25 may be permitted. K

yWhile one admirable form of the invention has been described in detail, and certainspecific i'lgures have been given, it will be understood `that the invention is capable of many modications and is applicable to a widevarietyoi-operating conditions. It-is noty desired-to be llmitedin'j its application f other :than 4:by the :scope of tthe i claims which follow: L

'What `I claim is:

1.In apparatus :for vconverting fhigher -iboiling xhydrncarbons into lower .boiling ones, a `.cylindrical stillgadapted to containa 'bodyfoffoiLa cylindrical shell -disposed Vwithin :the xstill jadapted to divide 4the latter into a relatively large inner `channel yand a relatively 'narrow annular ,passageway 'between said shell lland still, the :cross `sectional area xof ,'the inner channel `being relatively `larger than `that of -the k,fannular :passageway, I a propeller mounted within vthe inner lchannel-arranged Afor circulating oil lthrough :the inner and the annular channelsfata 4ratesuflicient to create turbulent Vflowyin the :annular passage- -Way `next -to .the wall .of 1the still, `and Lmeans for applying a heating medium -to .theexteror of the -wall of lthe still adjacent fthe annular passageway.'

2..In .apparatus for converting higher boiling hydrocarbons into lower boiling ones, a `heating coil adapted to heat `oil. intransit to-a cracking temperature under superatmospheric pressure, a cylindrical still `ladaptedto contain a .body of Yoil at cracking temperatures under superatmosphericpressure, a transfer line `adapted ltoXconduct oil from the heating ,coil -to the still, a cylindricalshell disposed within thefstill adapted to divide the latterintoa relatively large inner channel and a relatively narrow annularpassage- Way lbetween said Vshell and still, the'crosssectional area of the inner channel being relatively larger than that `of Vthe .annular passageway, a propeller mounted Within the inner channel .arranged for circulating .oil through the inner and the annular channelsata rate suiiicient to create turbulent ow in the Yannular passageway VVnext to the wall of the still, and meansfor applying Va `heating medium to Athe exterior of `the' wall ofthe still adjacent kvthe annular passageway.

3. vIn apparatus forconverting higher boiling hydrocarbons into lower boiling OneSVaplurality of cylindrical stills v.adapted to contain :bodies of oil at cracking temperatures under Vsuperatmospheric pressure, Vliquid .and .-.vapor lines .interconnecting the stillsin series, acylindricalshelldisposed within each still adapted to..divide.each still 'into a relatively .large inner channel and a relatively narrow annular passageway between ythe shell and still, the' cross sectional area of .the inner channels being relatively largerthan .that of the annular passageways, `propellers-mounted within the inner channels arrangedfor circulating oil through the inner Aand-annular channels at a rate sunicient to create turbulent flow in the annular passageways next to the walls `of the stills, and means for. applying a heating `me#Y dium to the yexterior of the `walls of the ,stills adjacent the annular Vpassageways I 4. In apparatusl for converting "'hig'her boiling hydrocarbonsinto lower boiling ones, a heating coil adapted to Zheat oil in transitto a cracking temperature under superatmospheric pressure,'a yplurality of cylindrical stills adapted tocontain bodies jof oil at cracking Vtemperatures under superatmospheric pressure, a transfer "line adapted to conduct oil fromrthe 'heating-coil -to one of the stills, liquid land .vapor I-lines interconnectingthe stills in.series,.a.cylindrical shell disposedwithin each stilladaptedtofdi-videzeach still into a relatively 'large innerrchannelz-.and arelatively narrow annular ipassageway between the shell and gstill, the cross-sectional1areafof `the inner channels being; relativelyylargenthan l.that

vofthe lannular passageways, .Propellers mounted Within the inner channels arranged forcirculatling-cil 'through -the `inner and annular Ychannels ata rate suflicient @to Icreate turbulent -flow tin .the 'annular passageways next to the 'Walls fof -the stil1s,and means for applying'a heating me- -dium to :the exterior ofthe walls of :the stills adjacent .the annular passageways 5. Thefprocess of continuously producing -gasoline :and `other light .oils from charging stock comprising heavier hydrocarbons, which convsists in continuously heating-such charging stock at a crackingtemperaturen a closed still; Isupplying .during the-run additionalcharging stock `to the'still; .continuouslytaking off vapors; lrejecting during the Arun part of the still contents; and forcing the entire liquidv'contents of the still vtherethrough under `the action of circulating `meansadapted to create `and-translate whirling vortexeffectsintofa positive driving forcewhereby such high velocity is obtained that -thefconditionsthroughout such still contents are,as to-tem- ,perature and'composition, sonearly identicalfthat variation Yas :to these characteristics in different parts of the still approaches the zero or vanishving point.

y6. Y The process Vof continuously producing gaso- -line and other .light oilsV from charging 4stock v comprising heavier hydrocarbons, which v consists `in continuously heating such charging stock'ata Ycracking'temperature in va closed still; continuously .supplying additional charging stock to gthe still; lcontinuously taking off vapors; withdraw- .ing during the-run a portion ofthe still contents;

and mechanically effecting such a turbulent andf rapid circulation-of the entire liquid contents of vcontinuously iiowing a stream of said `heavier hydrocarbons to and from acracking zone under pressure; extraneously heating a portionof said cracking zone; continuously releasing vaporized .hydrocarbons therefrom ytmnd-maintaining such a positiveand-rapid circulation ofthe hydrocarbons throughout the entire cracking zone independently of the stream of hydrocarbons flowingto .and

`from Vsaid cracking zonethat variation inconditions of temperature .and dispersion of solids throughout .the entire cracking zone approaches the zero or vanishing point.

8. In'anoil cracking still Vhaving afcirculating Apassage for the oil undergoing-crackinga propeller-having blades operating in said passage, .a tapered means in said passage immediately above the propeller for directing oil toward the center Y of saidblades and a rim surrounding said blades and in close proximity to the walls of said passage for preventing slippage of oilfrom saidpropeller blades back along the walls of.. said passage.

9. AIn an oil cracking still `having 4a .circulating vpassage -for 'the oil undergoing cracking,.a prov1.

Vpellerhavingblades operating in said passage,.a

rimfsurrounding said-blades for preventing slip- `page of oilfrom said'blades'back along the Walls of vsaid passage, land a. deecting cone overlying said rim iforfacilitating the 'flow of i oil vinto "said Y. blades.V

; tapered 'means associated '.with -isaidl passage -imrnediately above the propeller for directing oil toward the center of said blades, and a ring closely surrounding said blades for preventing slippage of oil from said propeller blades back along the Walls of said passage.

11. In an oil cracking still having a circulating passage for the oil undergoing cracking, `a propeller having blades operating in said passage, a

ring `closely `surrounding and coacting with said blades vfor preventing slippage of oil from said blades back along the walls of said passage, and a deflecting cone overlying said ring Afor facilitating the flow of oil into said blades. J

sage immediately above the propeller for directing Y oil toward the center of said blades, the outer edge of said propeller being in close proximity to the walls of said passage and underlapping the said'v tapered restriction to prevent slippage of oil from said propeller blades backv along the Walls of said 10' passage.

JOHN S. GALLAGHER. j 

